Ensure cache diretory exists before using roadrunner

[wyze]

Summary

This solves #1724. Ensures that we always have the cache directory created so roadrunner can work successfully.

Test plan

Not sure what kind of tests to add for this. @Daniel15, anything you can think of that could be added to e2e tests for this?

I was able to reduce the error with:

$ rm -rf ~/Library/Caches/Yarn
$ yarn --version

[Daniel15]

Running yarn --version before doing something like yarn add was one way to replicate the bug, right? In that case, you could simply add a yarn --version call to the top of the e2e test, around here: https://github.com/yarnpkg/yarn/blob/master/end_to_end_tests/data/run-yarn-test.sh#L15

[wyze]

Thanks for the direction. What I did will make the current e2e tests fail. If the fix applied in ./bin/yarn.js is merged, then it should work again.

I'll see if I can investigate a way to get this into a unit test as well.

[wellyshen]

The issue still exist, as I mentioned in #1724